Light and light sensor

ABSTRACT

A system of LED-based lights comprises first and second LED-based light having respective first and second electrical connectors configured for engagement with first and second conventional fluorescent fixtures, first and second LEDs configured to produce light in an area when the first and second electrical connectors are engaged with the first and second fixtures and first and second controllers electrically coupled to the first and second LEDs; and one or more sensors operable to detect a brightness level in the area and output respectively one or more signals indicative of the brightness level, wherein: the first and second controllers are configured to control an amount of power provided to the respective first and second LEDs at least partially based on a signal to adjust the light produced in the area towards a desired brightness level.

STATEMENT OF RELATED CASES

This application is a continuation of U.S. patent application Ser. No.13/829,069, filed on Mar. 14, 2013, which is a continuation-in-part ofU.S. patent application Ser. No. 13/690,609, filed Nov. 30, 2012, whichis a continuation of U.S. patent application Ser. No. 12/572,471, filedOct. 2, 2009, and now U.S. Pat. No. 8,324,817, which claims priorityfrom U.S. Provisional Patent Application Ser. No. 61/108,354 filed Oct.24, 2008, all of which are hereby incorporated by reference in theirentireties.

FIELD

An LED-based light as described herein relates to “smart buildings” thatcan automatically control lighting in response to various environmentalconditions.

BACKGROUND

Lights in buildings are generally controlled by switches, such aswall-mounted switches in the vicinity of one or more lights. The switchcan include a dimmer for varying the brightness of one or more lights.However, lights are often left on when not needed, such as when nopeople are around the lights or when sources of light besides the lights(e.g., sunlight passing through windows and/or skylights) providesufficient illumination.

SUMMARY

Known smart buildings that can automatically control variousenvironmental characteristics, such as a lighting brightness level, ofone or more rooms of a building are typically expensive to manufactureand install. For example, known smart building components typically arenot compatible with standard building fixtures, such as conventionalfluorescent tube fixtures, and thus can require an electrician toinstall.

Embodiments of LED-based lights described herein can be used totransform a building with standard fixtures, such as standardfluorescent tube fixtures, into a smart building. Many advantages areoffered by the LED-based lights described herein, such as allowing for alow-cost smart building and automatically providing an alert when anefficiency of the LED-based light becomes too low.

In one embodiment, a system of LED-based lights comprises: a firstLED-based light having a first electrical connector configured forengagement with a first conventional fluorescent fixture, a first LEDconfigured to produce light in an area when the first electricalconnector is engaged with the first fixture and a first controllerelectrically coupled to the first LED; a second LED-based light having asecond electrical connector configured for engagement with a secondconventional fluorescent fixture, a second LED configured to producelight in the area when the second electrical connector is engaged withthe second fixture and a second controller electrically coupled to thesecond LED; and one or more sensors operable to detect a brightnesslevel in the area and output respectively one or more signals indicativeof the brightness level, wherein: the first and second controllers areconfigured to control an amount of power provided to the respectivefirst and second LEDs at least partially based on a signal to adjust thelight produced in the area towards a desired brightness level.

In another embodiment, a system for measuring an efficiency of aplurality of LED-based lights comprises: a first LED-based light havinga first electrical connector compatible with a first standardized lightfixture, a first LED configured to produce light in an area when thefirst electrical connector is engaged with the first fixture and a firstcontroller electrically coupled to the first LED; a second LED-basedlight having a second electrical connector compatible with a secondstandardized light fixture, a second LED configured to produce light inthe area when the second electrical connector is engaged with the secondfixture and a second controller electrically coupled to the second LED;and one or more sensors operable to detect a brightness level in thearea and output respectively one or more signals indicative of thebrightness level, wherein: the brightness level in the area is afunction of the light produced by the first and second LEDs, and atleast one of the first and second controllers is operable to estimate anefficiency of the system of LED-based lights at least partially based onthe brightness level in the area.

These and other embodiments will be described in additional detailhereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of an LED light tube;

FIG. 2 is a schematic perspective view of a smart building system;

FIG. 3 is a schematic perspective view of yet another example of an LEDlight tube;

FIG. 4 is a flowchart illustrating operation of an example of an LEDlight tube;

FIG. 5 is a schematic perspective view of another example of a smartbuilding system; and

FIG. 6 is a flowchart illustrating operation of multiple LED lighttubes.

DESCRIPTION

FIGS. 1-6 are discussed in reference to a light and a light sensor. Asshown in FIG. 1, a light fixture 14 can accept an LED-based light 16.The light fixture 14 can be designed to accept standard fluorescenttubes, such as a T-5, T-8, or T-12 fluorescent tube, or other standardsized light, such as incandescent bulbs. Alternatively, the fixture 14can be designed to accept non-standard sized lights, such as lightsinstalled by an electrician.

The LED light tube 16 can include a housing 22, a circuit board 24, LEDs26, a pair of end caps 28, a controller 25, and a receiver 27 as shownin FIG. 1. The housing 22 as shown in FIG. 1 is a light transmittingcylindrical tube. The housing 22 can be made from polycarbonate,acrylic, glass or another light transmitting material (i.e., the housing22 can be transparent or translucent). For example, a translucenthousing 22 can be made from a composite, such as polycarbonate withparticles of a light refracting material interspersed in thepolycarbonate. While the illustrated housing 22 is cylindrical, housingshaving a square, triangular, polygonal, or other cross sectional shapecan alternatively be used. Similarly, while the illustrated housing 22is linear, housings having an alternative shape, e.g., a U-shape or acircular shape can alternatively be used. Additionally, the housing 22need not be a single piece as shown in FIG. 1. Instead, another exampleof a housing can be formed by attaching multiple individual parts, notall of which need be light transmitting. For example, such a housing caninclude an opaque lower portion and a lens or other transparent coverattached to the lower portion to cover the LEDs 26. The housing 22 canbe manufactured to include light diffusing or refracting properties,such as by surface roughening or applying a diffusing film to thehousing 22. For compatibility with the fixture 14 as discussed above,the housing 22 can have a length such that the light 16 is approximately48″ long, and the housing 22 can have a 0.625″, 1.0″, or 1.5″ diameter.

The circuit board 24 as illustrated in FIG. 1 is an elongate printedcircuit board. Multiple circuit board sections can be joined by bridgeconnectors to create the circuit board 24. The circuit board 24 as shownin FIG. 1 is slidably engaged with the housing 22, though the circuitboard 24 can alternatively be clipped, adhered, snap- or friction-fit,screwed or otherwise connected to the housing 22. For example, thecircuit board 24 can be mounted on a heat sink that is attached to thehousing 22. Also, other types of circuit boards may be used, such as ametal core circuit board. Or, instead of a circuit board 24, other typesof electrical connections (e.g., wires) can be used to electricallyconnect the LEDs 26 to a power source.

The light 16 can include two bi-pin end caps 28 (i.e., each end cap 28can carry two pins), one at each longitudinal end of the housing 22, forphysically and electrically connecting the light 16 to the fixture 14.The end caps 28 can be the sole physical connection between the light 16and the fixture 14. The end caps 28 can be electrically connected to thecircuit board 24 to provide power to the LEDs 26. Each end cap 28 caninclude two pins, though two of the total four pins can be “dummy pins”that do not provide an electrical connection. Alternatively, other typesof electrical connectors can be used, such as an end cap carrying asingle pin. Also, while the end caps 28 are shown as includingcup-shaped bodies, the end caps 28 can have a different configuration(e.g., the end caps 28 can be shaped to be press fit into the housing22). One or both of the end caps 28 can additionally include electriccomponents, such as a rectifier and filter.

The LEDs 26 can be surface-mount devices of a type available fromNichia, though other types of LEDs can alternatively be used. Forexample, although surface-mounted LEDs 26 are shown, one or more organicLEDs can be used in place of or in addition thereto. The LEDs 26 can bemounted to the circuit board 24 by solder, a snap-fit connection, orother means. The LEDs 26 can produce white light. However, LEDs thatproduce blue light, ultra-violet light or other wavelengths of light canbe used in place of white light emitting LEDs 26.

The number of LEDs 26 can be a function of the desired power of thelight 16 and the power of the LEDs 26. For a 48″ light, such as thelight 16, the number of LEDs 26 can vary from about five to four hundredsuch that the light 16 outputs approximately 500 to 3,000 lumens.However, a different number of LEDs 26 can alternatively be used, andthe light 16 can output a different amount of lumens. The LEDs 26 can beevenly spaced along the circuit board 24, and the spacing of the LEDs 26can be determined based on, for example, the light distribution of eachLED 26 and the number of LEDs 26.

The controller 25 can be mounted on the circuit board 24, and caninclude a memory and a CPU for executing a program stored on the memory.That is, the controller 26 can be include a microprocessor or otherdigital or analog circuit that performs the tasks described herein. Thecontroller 25 can be in communication with the LEDs 26, the end caps 28,and the receiver 27 via the circuit board 24, though the controller 25can alternatively be in communication with the LEDs 26, end caps 28,and/or receiver 27 using wires or another connection. The controller 25can also be configured to regulate the amount of power provided to theLEDs 26. That is, the controller 28 can govern the amount of powerprovided from the end caps 28 to the LEDs 26. The controller 28 can bein communication with multiple subsets of LEDs 26 (such as individualLEDs 26) for providing a different amount of power to one or more of thesubsets of LEDs 26. Alternatively, a controller can be external of thelight 16. For example, a controller can be coupled to the fixture 14 tocontrol a light attached to the fixture 14.

The light 16 can additionally include a receiver 27 mounted on thecircuit board 24. The receiver 27 can be in communication with thecontroller 25 as mentioned above and with a remote transmitter as isdiscussed below in greater detail. For example, the receiver 27 can bein communication with the transmitter using a standard wireless protocol(e.g., a radio standard, a cellular standard such as 3G, Bluetooth, orWiFi). The receiver 27 can alternatively be in communication with thetransmitter in another manner such as hardwiring or via electric signalssent through the end caps 28. The receiver 27 can be configured toreceive signals from the transmitter, and the receiver 25 can transmitreceived signals to the controller 25.

While the light 16 is shown as being compatible with standard sizedfluorescent fixtures, an LED-based light having another shape, such asan incandescent bulb or another type of light, can alternatively beused. Also, other types of light sources, such as fluorescent orincandescent based light sources, can be used instead of the LEDs 26.

As illustrated in FIG. 2, the fixture 14 can be in a building 11including a light switch 31 and a light sensor 33, and the light 16 canbe installed in the fixture 14. The light switch 31 can control whetherpower is provided to the fixture 14. However, as is mentioned above anddescribed below in greater detail, the controller 25 can control whetherpower is provided to the LEDs 26, in which case the light switch 31 neednot be included. Also, if the building 11 is a “smart” building, thecontroller 25 and switch 31 can be in communication (e.g., via a wiredconnection, or via a wireless transmitter and a wireless receiver) suchthat the controller 25 can override the switch 31 to turn on the light16 even when the switch 31 is in an off position or vice versa.

The light sensor 33 can detect a level of light in an area of thebuilding 11 including the light 16, such as an amount of light thatstrikes the sensor 33. The light sensor 33 can include an integraltransmitter for transmitting a light level signal α to the receiver 27.The light sensor 33 can continuously transmit the signal, or the lightsensor 33 can include a controller (e.g., a controller including amemory and a CPU for executing a program stored on the memory) fordeciding when to transmit the signal. In addition to the light sensor33, other sensors can be in communication with the light 16. Forexample, the building 11 can also include a motion sensor, a sensor fordetermining whether a door is ajar, a sensor for determining when akeypad or other type of lock is actuated, a voice-activated sensor, aclock or calendar, a light sensor for measuring an amount of light inthe building 11 other than or including light provided by the light 16(e.g., an amount of sunlight entering the building 11), a power supplymonitor, and/or another type of sensor.

In operation, as shown by in FIG. 4, the light 16 produces light in stepS1. In step S2 the light sensor 33 can measure the amount of light thatstrikes the sensor 33, and the light sensor 33 can transmit the lightlevel signal α to the receiver 27 as shown in step S3. The receiver 27can communicate the light level signal α to the controller 25 as shownin step S4.

In step S5, the controller 25 can analyze the light level signal α. Forexample, the controller 25 can estimate a brightness of an area of thebuilding 11 including the light 16, the controller 25 can compare thelight level to a predetermined value (e.g., an amount of lightcomfortable for an ordinary person), or can analyze the light levelsignal α in some other manner. Depending on the light level signal α,the controller 25 can control the light 16 in various ways. For example,as shown in step S6, the controller 25 can adjust the brightness oflight produced by the LEDs 26. If the light level signal α indicates theamount of light detected is too high, the controller 25 can dim the LEDs26 or turn a subset of the LEDs 26 off. Alternatively, if the amount oflight is too low, the controller 25 can increase the brightness of theLEDs 26 or turn on a subset of the LEDs 26 that were previously off.Thus, the controller 25 can correct the amount of light provided by thelight 16 in response to changes in ambient light, such as if a level ofnatural light entering the area of the building 11 including the light16 increases or decreases, or if other lights are turned on or off.

In another example not illustrated, the light 16 can initially not beproducing light. The controller 25 can control the light 16 to beginproducing light in response to the light level signal α. For example,the light level signal α can indicate that the amount of light in anarea of the building 11 is below a predetermined level.

To avoid interference with the light sensor 33 by the light emitted bythe LEDs 26, the light sensor 33 can sense ambient light during a shortperiod, invisible to the eye, when the LEDs 26 are off. This short offperiod can occur due to line voltage zero-crossing, or a command fromthe controller 25.

Therefore, among other advantages, an occupant of the area of thebuilding 11 including the light 16 can avoid having to make an effort toturn on the light.

Returning to FIG. 4, as another example of operation of the light 16shown in step S7, the light level signal α can be analyzed by thecontroller 25 to determine an efficiency of the light 16. For example,the controller 25 can compare the amount of detected light with areference value, such as an amount of light detected at a previous dateif the light 16 includes a clock and/or calendar. The previous date canbe a date when conditions such as ambient light conditions were similar,such as a recent day at approximately the same time. The differencebetween the current amount of light being produced and the previousamount of light being produced can be used to calculate a change inefficiency of the light 16. The controller 25 can make this efficiencydetermination without turning the light 16 off, which can be beneficialif the light 16 is in a location such as a stairwell where a lack oflight can be dangerous. As an alternative efficiency test, thecontroller 25 can compare the amount of detected light when the light 16is on with an amount of light detected when the light 16 is off, withthe difference being used to calculate an amount of light produced bythe light 16.

The controller 25 can calculate the efficiency by comparing the amountof light produced by the light 16 with the reference value (e.g., anamount of light produced by the light 16 operating under idealconditions), or by comparing the amount of light produced by the light16 with the amount of power consumed by the light 16 (which can bemeasured with an ammeter and voltmeter, a wattmeter, or another powermeasuring device either integral with the light 16, electrically coupledto the fixture 14, or at another location).

As shown in step S8, the controller 25 can also determine whether thelight 16 should be replaced. For example, the controller 25 can comparethe efficiency of the light 16 with a predetermined value to determinewhether the light 16 should be replaced. The predetermined value can bea predetermined efficiency standard, such as the efficiency of the light16 when new, the efficiency of an ideal light, a maximal output of thelight 16, or some other value.

The controller 25 can also control the light 16 to indicate itsefficiency, which can provide notice that the light 16 should bereplaced. For example, the controller 25 can control the light 16 todisplay its efficiency using a digital read-out integral with the light16, a bar of light having a length equivalent with the efficiency, or inanother manner. Alternatively, the controller 25 can control the light16 to display when the efficiency of the light 16 is below apredetermined value, such as by illuminating at least one of the LEDs 26having a different color than surrounding LEDs 26, by causing at leastone of the LEDs 26 to flash, or by controlling the light 16 in someother manner. Once the efficiency of the light 16 drops below thepredetermined value, it can be understood that the light 16 should bereplaced. Thus, the light 16 can signal to a maintenance worker or otherpersonnel that the light 16 should be replaced.

Another light 40 as shown in FIG. 3 includes the housing 22, the circuitboard 24, the controller 25, the LEDs 26, and the end caps 28 similar tothe light 16. The light 40 can additionally include an integral lightlevel sensor 42 and a transmitter 44. The light sensor 42 can be mountedon the circuit board 24 to receive power via the end caps 28, and thelight sensor 42 can be in communication with the controller 25 and/orthe transmitter 44. The light level sensor 42 can protrude from thehousing 22 as shown in FIG. 3 or otherwise be positioned to sense anamount of light produced by at least some of the LEDs 26 (e.g., thesensor 42 can alternatively be contained within the housing 22, and oneor more reflectors can be included to direct a portion of light towardthe sensor 42). Alternatively, the light level sensor 42 can detect anamount of ambient light. The amount of ambient light can include lightproduced by the LEDs 26. The sensor 42 can communicate the light levelsignal α to the controller 25.

The transmitter 44 can be mounted on the circuit board 24 for receivingpower via the end caps 28. The transmitter 44 can be in communicationwith the controller 25 and/or the light sensor 24 for receiving thelight level signal α. The transmitter 44 can be configured to transmitthe light level signal α to a remote location, such as a smart buildingcontrol center or another smart building component, or to controllers 25of other lights 16, 40.

With this configuration, the controller 25 in the light 40 can controlthe LEDs 26 and calculate an efficiency of the light based on the lightlevel signal α as discussed above in reference to the light 16. Thelight 40 can also indicate whether the light 40 should be replacedsimilar to as described above in reference to the light 16.Additionally, the inclusion of the transmitter 44 allows the light 40 toperform other functions. The transmitter 44 can transmit the light levelsignal α to the remote location, allowing the light level signal α to beused for controlling another component of a smart building (e.g., windowshades, another light, or some other component of a smart building) orfor another purpose. For example, the transmitter 44 can transmit anefficiency of the light 40 or an indication that the light 40 should bereplaced to the remote location.

The light 40 can also include another sensor, such as a motion detector,in communication with the controller 25 and/or the transmitter 44. Inthis case, the controller 25 can take signals other than the light levelsignal α into consideration in controlling the LEDs 26. For example, thecontroller 25 can turn the LEDs 26 off even though the light levelsensor 42 detects a low level of light if the motion sensor has notdetected movement for a certain amount of time. As a similar example,the controller 25 can turn the LEDs 26 off even though the light levelsensor 42 detects a low level of light if a clock or calendar incommunication with the controller 25 indicates the time is not duringstandard working hours.

As illustrated in FIG. 5, multiple fixtures 14 can be in the building 11including the light switch 31 and the light sensor 33, and multiple ofthe lights 16 and/or 40 described above can be installed in the fixtures14. Each light 16, 40 may include a controller 25 configured to regulatethe amount of power provided to the respective LEDs 26, as describedabove. The controllers 25 can be external of the lights 16, 40, forexample, coupled to a fixture 14 to control a light 16, 40 attached tothe fixture 14. It will be understood that a controller 25 can beprovided that performs the tasks described herein with respect tomultiple of the lights 16, 40, for example, those installed in a commonfixture 14.

In operation, as shown by in FIG. 6, one or more of the lights 16, 40produce light in step S61. In step S62, the light sensor 33 can measurethe amount of light that strikes the sensor 33, and transmit a lightlevel signal α to one or more of the lights 16, 40. In addition, or inthe alternative, if a light 40 is installed, the light sensor 42 of thelight 40 can measure the amount of light that strikes the sensor 42, andtransmit a light level signal α. It can therefore be seen that the lightlevel signals α in this example may be generated by a remote sensor 33,or by a light sensor 42 of a light 40. Additionally, the light levelsignals α may be a function of multiple of the lights 16 and/or 40. Eachsignal light level signal α may be indicative of the light produced byone light 16, 40, multiple lights 16, 40 or all lights 16, 40, andcollectively, the light level signals α are indicative of the overalllighting conditions in the building 11. The light level signal α (oroptionally multiple light level signals α of more than one sensor 33,42, depending upon the specific configuration for the building 11) canbe transmitted to one or more of the receivers 27 as shown in step S63.

The receivers 27 can communicate the light level signal(s) α to thecontrollers 25 for processing and analysis as shown in step S64. In oneexample, multiple controllers 25 (e.g., one controller 25 for each light16, 40) may exist in the system. The signal(s) α may be used among thecontrollers 25 to generate control signals indicative of the desiredcontrol for the LEDs 26 of the respective lights 16, 40 according to theoperations described herein. For instance, each of the respectivecontrollers 25 of the lights 16, 40 may communicatively receive one ormore of the signals α for individual analysis, as generally describedabove, and then control the LEDs 26 of the respective lights 16, 40.This analysis and control may be performed collaboratively with respectto the analysis and control of other controllers 25, for instance.Alternatively, fewer than all of the controllers 25 can be performcertain of the tasks described herein, and can communicate with othercontrollers 25 of the respective lights 16, 40 to effect control of theLEDs 26, for instance, via transmitters 44 and receivers 27. However, inanother example, the lights 16, 40 need not have individual controllers25 where, for instance, a controller 25 is external of the lights 16, 40and coupled to a fixture 14 common to multiple lights 16, 40.

In step S65, the one or more light level signals α are analyzed by thecontrollers 25. For example, the brightness of an area of the building11 including the lights 16, 40 can be estimated, and the light level canbe compared to a predetermined value (e.g., an amount of lightcomfortable for an ordinary person), or the light level signal(s) α canbe analyzed in some other manner. The light level signals α may beanalyzed to estimate an overall brightness of the area of the building11, for example, or could be analyzed to estimate multiple brightnesslevels within the area. Depending on the light level signal(s) α, thelights 16, 40 may be controlled in various ways. For example, as shownin step S66, the controllers 25 can collectively function to adjust thebrightness of light produced by the LEDs 26 of the lights 16, 40. Withrespect to each of the individual lights 16, 40, if the amount of lightdetected is too high, a controller 25 can dim the LEDs 26 or turn asubset of the LEDs 26 off. Alternatively, if the amount of light is toolow, a controller 25 can increase the brightness of the LEDs 26 or turnon a subset of the LEDs 26 that were previously off. A control schemeaccounting for multiple of the lights 16, 40 may also cause the LEDs 26of one or more lights 16, 40 to be dimmed or brightened, or turned on oroff, in accordance with a desired brightness level. Thus, thecontrollers 25 can collectively correct the amount of light provided bythe lights 16, 40 in response to changes in ambient light, such as if alevel of natural light entering the area of the building 11 includingthe lights 16, 40 increases or decreases, or if other lights are turnedon or off.

In another example not illustrated, one or more of the lights 16, 40 caninitially not be producing light. The controllers 25 can control thelight 16, 40 to begin producing light in response to the light levelsignal(s) α. For example, the light level signal(s) α can indicate thatthe amount of light in an area of the building 11 is below apredetermined level.

To avoid interference with the light sensors 33, 42 by the light emittedby the LEDs 26 of the lights 16, 40, the light sensors 33, 42 can senseambient light during a short period, invisible to the eye, when the LEDs26 are off. This short off period can occur due to line voltagezero-crossing, or via commands from the controllers 25.

Therefore, among other advantages, an occupant of the area of thebuilding 11 including the light 16, 40 can avoid having to make aneffort to turn on the lights.

In FIG. 6, as another example of operation of the lights 16, 40 shown instep S67, the light level signal(s) α can be analyzed to determine anefficiency of the lights 16, 40, either individually or on a collectivebasis. For example, the controllers 25 can collectively function tocompare the amount of detected light with a reference value, such as anamount of light detected at a previous date. The previous date can be adate when conditions such as ambient light conditions were similar, suchas a recent day at approximately the same time. The difference betweenthe current amount of light being produced and the previous amount oflight being produced can be used to calculate a change in efficiency ofthe lights 16, 40. The controllers 25 can make this efficiencydetermination without turning the lights 16, 40 off, which can bebeneficial if the lights 16, 40 are in a location such as a stairwellwhere a lack of light can be dangerous. As an alternative efficiencytest, the controllers 25 can compare the amount of detected light whenthe lights 16, 40 are on with an amount of light detected when thelights 16, 40 are off, with the difference being used to calculate anamount of light produced by the lights 16, 40. The controller 25 cancalculate the efficiency by comparing the amount of light produced bythe lights 16, 40 with the reference value (e.g., an amount of lightproduced by the lights 16, 40 operating under ideal conditions), or bycomparing the amount of light produced by the lights 16, 40 with theamount of power consumed by the light 16, 40 (which can be measured withan ammeter and voltmeter, a wattmeter, or another power measuring deviceeither integral with the lights 16, 40, electrically coupled to thefixtures 14, or at another location).

It will be understood that the comparisons described above can becompleted with respect to individual lights 16, 40, for example, or withrespect to subsets of lights 16, 40 or all lights 16, 40 collectively.Where less than all of the lights 16, 40 are under consideration, forinstance, the output of those lights 16, 40 may be factored out of theanalysis, e.g., by turning the lights 16, 40 off or by otherwiseaccounting for their light output, power consumption, etc.

As shown in step S68, the controllers 25 can also determine whether oneor more of the lights 16, 40 should be replaced. For example, thecontroller 25 can compare the efficiency of the lights 16, 40 with apredetermined value to determine whether one, some of all of the lights16, 40 should be replaced. The predetermined value can be apredetermined efficiency standard, such as the efficiency of the lights16, 40 when new, the efficiency of an ideal light, a maximal output ofthe lights 16, 40 or some other value. The determination in this stepmay be made according to individual lights 16, 40, for example, or withrespect to subsets of lights 16, 40 or all lights 16, 40 collectively.

As shown in step S69, the controllers 25 can also control the lights 16,40 to indicate efficiency, which can provide notice that one, some, orall of the lights 16, 40 should be replaced. For example, thecontrollers 25 can control one or more lights 16, 40 to displayefficiency using a digital read-out integral with the lights 16, 40, abar of light having a length equivalent with the efficiency, or inanother manner. Alternatively, the controllers 25 can control the lights16, 40 to display when the efficiency of the lights 16, 40 is below apredetermined value, such as by illuminating at least one of the LEDs 26of a respective light 16, 40 having a different color than surroundingLEDs 26, by causing at least one of the LEDs 26 to flash, or bycontrolling the lights 16, 40 in some other manner. Once the efficiencyone or more lights 16, 40 drops below a predetermined value, it can beunderstood that the lights 16, 40 should be replaced. Thus, the lights16, 40 can signal to a maintenance worker or other personnel when one ormore of the lights 16, 40 should be replaced. Once again, it will beunderstood that the indication of efficiency in this step may be madeaccording to individual lights 16, 40, for example, or with respect tosubsets of lights 16, 40 or all lights 16, 40 collectively.

The above-described embodiments have been described in order to alloweasy understanding of the invention and do not limit the invention. Onthe contrary, the invention is intended to cover various modificationsand equivalent arrangements included within the scope of the appendedclaims, which scope is to be accorded the broadest interpretation so asto encompass all such modifications and equivalent structure as ispermitted under the law.

What is claimed:
 1. A system of LED-based lights, comprising: a firstLED-based light having a first electrical connector configured forengagement with a first conventional fluorescent fixture, a first LEDconfigured to produce light in an area when the first electricalconnector is engaged with the first fixture and a first controllerelectrically coupled to the first LED; a second LED-based light having asecond electrical connector configured for engagement with a secondconventional fluorescent fixture, a second LED configured to producelight in the area when the second electrical connector is engaged withthe second fixture and a second controller electrically coupled to thesecond LED; and one or more sensors operable to detect a brightnesslevel in the area and output respectively one or more signals indicativeof the brightness level, wherein: the first and second controllers areconfigured to control an amount of power provided to the respectivefirst and second LEDs at least partially based on a signal to adjust thelight produced in the area towards a desired brightness level.